1. Field of the Invention
The present invention relates generally to systems for forming concrete. More specifically, the present invention concerns a forming system having a displaceable panel for forming the concrete that is vibrated relative to a stationary frame to compact the concrete. The forming system of the present invention is particularly well suited for forming box culverts. In a preferred embodiment, a plurality of the displaceable panels are independently supported on modular frames by a specified number of springs that enable each of the panels to be vibrated at or about a resonant frequency, thereby providing optimum external concrete compaction. The inventive forming system enables denser, stronger finished concrete to be formed with lighter weight, lower maintenance frames that are longer lasting than previous systems.
2. Discussion of Prior Art
Those ordinarily skilled in the construction industry will appreciate that when forming concrete, it is desirable to reduce the air voids in the wet concrete to a minimum in order to obtain a denser mass for the finished, hardened concrete. Air voids are reduced by compacting the concrete. Compaction can occur internally (e.g., by stirring the concrete), externally (e.g., by vibrating the concrete itself), or with the use of a table (e.g., by vibrating the entire form). In relatively larger forming applications, compaction is primarily accomplished externally and its impact is directly related to both the amplitude and frequency of the vibration. One such application is pre-cast concrete box culverts. Pre-cast concrete box culverts are a desired solution over cast-in-place culverts for a wide variety of applications such as highway bridges and drainage conditions, such as storm and sanitary sewers. These pre-cast culverts come in a variety of sizes (e.g., various rises, spans, thicknesses, etc.) but typically come in relatively large, standard lengths, such as six, eight and ten feet and have a typical thickness of about one-half meter. The culverts can be joined together lengthwise at the ends (e.g., with mastic, gaskets, etc.) to form the desired run.
Forming systems for forming the pre-cast concrete box culverts are known in the art. These prior art forming systems typically include modular components, such as cores, jackets, and pallets, in combination with some type of header. One example of such a forming system is disclosed in the Application for U.S. Letters patent Ser. No. 10/279,255, entitled MODULAR FORMING SYSTEM FOR BOX CULVERT, filed Oct. 23, 2002 (having a common inventor and assigned to the same assignee as the present application and hereinafter “the '255 Application”), which is hereby incorporated herein by reference. The forming system disclosed in the '255 Application was an advance in the art at the time and included easily assembled modular components, including a modular header. The forming system of the '255 Application, however, like all prior art forming systems for box culverts, utilized rigidly formed jacket sections that are vibrated with one or more eccentric motors. These systems provide some amplitude that facilitates compaction, but do not enable the desired frequencies to provide a more optimum compaction of the concrete.
It is also known in the art of forming concrete to form the concrete in a rigid form that is supported on a vibrating table. However, like the systems described above, the vibrating tables simply do not provide the desired frequency to enable compaction throughout the concrete. Additionally, the tables are limited in their application and are not well suited for relatively larger forms. Vibrating screeds are also known in the art for finishing concrete and typically include a portable frame and an adjustable panel fixed to the frame that are both vibrated by a motor. The screeds are typically moved over the finishing surface only. In this regard, the screeds do not form any of the other surfaces and are not suited for compacting larger concrete applications such as the box culverts discussed above.
These prior art forming systems are problematic and subject to several limitations. For example, as indicated above, the forming systems simply cannot provide the necessary frequencies throughout the thickness of the concrete to optimize compaction. In this regard, as applied to box culverts, the concrete formed in these prior art systems must typically be mixed at least in a ratio of 1:3 water to dry mix. However, a dryer mix is more desirable as it enables a denser and thus stronger finished product. Additionally, the prior art forming systems are typically associated with high maintenance costs and reduced longevity of the frames, as well as the vibrators. These limitations are largely attributable to the vibration of the rigid forming sections, as well as the amplitude of the vibration used. Furthermore, during vibration of the forms, the bolts that hold the jacket together are undesirably prone to becoming loose and thereby compromising the mold, therefore, prior art jackets typically include heavy, rigid frames to compensate for this limitation. These problems and limitations are undesirable in that they add increased labor and/or expense to manufacturing, assembling, and maintaining the forming systems.